Such a filter device comprises a circular adapter, having at least one means for connecting a filter cartridge. The connecting means protrudes downwards from said adapter. A circular head joins integrally to and is positioned above the adapter. The circular adapter and the circular head have a common outer periphery. A distribution compartment is positioned between the head and the adapter. A sealing device is in the area of the outer periphery. A clamping surface is in the area of the outer periphery and is adapted to press against the top region of a flexible filter bag.
Such a device became known in the prior art from German OS No. 3,520,139, which corresponds to U.S. Pat. No. 4,711,717 of the same inventor.
Such a device filters very harmless media, but also extremely dangerous media. It is clear that the sealing plays a very great part. The known device had the following disadvantages:
(a) An O-ring 34 is used which is subject to tension stress to retain it in its groove. Thus it varies its properties in the course of time.
(b) The O-ring 34 additionally had the task of holding the end zone 29 of the flexible bag 16. In doing so, it loses sealing quality. Insofar as the end zone 29 can be drawn over the outer surface 28 and lies in the seating groove of the O-ring 34, it has a smaller diameter and consequently forms folds.
(c) The O-ring 34 must develop extraordinarily great tension forces if it is to hold a fluid-filled flexible bag 16 when the adapter is to be removed from the bowl 17. At that moment, the whole weight hangs on the O-ring 34.
(d) A separate head 78 and an adapter 62 are necessary. A separation surface lies between the two. One seeks to keep the outer edge sealed by drawing the lid 84 against the bowl 69. Since, however, these parts are injection-moldings, which do not tolerate excessively high-grade production, the surfaces are uneven. This must be compensated by extraordinary high pressure. If, however, an extraordinary high pressure is exerted upon synthetic plastic material, the material flows in the course of time. If it flows, the sealing quality deteriorates.
(e) If one takes the head 78 off, surfaces previously wetted by the fluid are exposed. In the case of toxic substances this is very dangerous. Even in the case of non-dangerous substances this leads to a substantial cleaning effort.
(f) The head 78 too has to be cleaned before it is used with a new adapter 62.
(g) Pressures occurring in the fluid distribution compartment can bend the adapter 62 downwards, which leads to fluid short-circuits, working the O-ring and causing pivoting movements of the filter cartridges. This occurs because the adapter 62 domes into a partial sphere.
(h) The device for drawing the clamping plate 84 and the clamping ring 83 against one another must be extraordinarily strong. This leads to over-thickness, weight, clumsiness and high price.
(i) The sealing areas must be extraordinarily large, and a great deal of material is situated around the sealing areas, making the device expensive. High material expense is, however, undesirable in non-reusable devices.
(j) If one were to use two flexible bags--one for safety outside the other that retains the fluid--it would be much too great a task for the O-ring 34.